1. Field of the Invention
The present invention relates generally to disk drives, and more particularly relates to improving data integrity in disk drives.
2. Description of the Related Art
One of the key components in a computer system is the place to store and retrieve data. Typically, computer systems employ a number of storage means, including a disk drive which may be referred to as a direct access storage device (DASD). A disk drive includes several disks stacked on a spindle. The disks are mounted to the spindle in a spaced-apart relationship so that the separate disks do not touch each other. Both sides of each disk are generally used to store data.
Each disk surface is divided into portions where data is stored. There are a number of tracks situated in concentric circles, and each track in a disk drive is further subdivided into a number of sectors which generally comprise a section of the circumferential track. Disks in a disk drive are made of a variety of materials; most commonly, the disk is made of metal, plastic, or glass. To store and retrieve data on a disk, a magnetic transducer known as a read/write head is passed over the surface of the disk. The digital data stored on a disk is represented as a series of variations in magnetic orientation of the disk magnetic material. The variations in magnetic orientation, generally comprising reversals of magnetic flux, represent binary digits of ones and zeroes that in turn represent data. The binary digits must be read from and recorded onto the disk surface in close proximity to the disk. The transducer or read/write head is provided to produce and detect variations in magnetic orientation of the magnetic material as the disk rotates relative to the head.
Positioning read/write heads is one of the most critical aspects of recording and retrieving data in disk storage systems. With the very high track density of current disk drives, even the smallest head positioning error can potentially cause a loss of data that a disk drive customer wants to record or read.
The read/write head is mounted on a disk arm that is moved across the disk by a servo. A disk drive servo control system controls movement of the disk arm across the surface of the disk to move the read/write head from data track to data track and, once over a selected track, to maintain the head in a path over the centerline of the selected track. Maintaining the head centered over a track facilitates accurate reading and recording of data in the track.
A servo control system generally maintains a read/write head in a position centered over a track by reading servo information recorded onto the disk surface. The servo read head can be the same head used for reading data or can be a separate, dedicated servo head. The servo information comprises a position-encoded servo pattern of high frequency magnetic flux transitions, generally flux reversals, that are pre-recorded in disk servo tracks. The flux transitions are recorded as periodic servo pattern bursts formed as parallel radial stripes in the servo tracks. When the read/write head passes over the servo pattern flux transitions, the head generates an analog signal whose repeating cyclic variations can be demodulated and decoded to indicate the position of the head over the disk. The demodulated servo signal is referred to as a position error signal (PES). The PES is used to generate a corrective input signal that is applied to the read/write head positioning servo. Thus, data may be read from and recorded to the appropriate track with a good degree of accuracy. A write inhibit signal is used to terminate transmission of a write signal to a head during a time period that the servo signal indicates that the head is off center by an amount that would result in writing data in an adjacent track.
Although such measures are taken for accurate positioning of the heads, some portions of adjacent tracks may still be inadvertently written along during writes to target tracks. Such inadvertent writing adversely affects the signal-to-noise (SNR) ratio of these adjacent tracks and thus data errors may result during subsequent reads. The errors may be referred to xe2x80x9csoft errors,xe2x80x9d where data recovery is possible, or xe2x80x9chard errors,xe2x80x9d where the errors are so severe that data recovery is not possible. Errors become more likely when such interference undesirably resides on both sides of a track. Continuing efforts to decrease the width of magnetic heads exacerbate this xe2x80x9csqueeze hard errorxe2x80x9d problem, since error tolerances associated with head width generally increase in cost-effective designs.
Thus, what is needed is a method and apparatus for improving data integrity in a disk drive system, and especially one that solves the aforementioned deficiencies of the prior art.
A method of and apparatus for improving data integrity in a disk drive system is disclosed. In response to a write fault, it is determined whether an excessive track overshoot condition exists based on current head position, head width, and threshold criteria. If an excessive track overshoot condition exists, data is read from and rewritten to one or more tracks adversely affected thereby. Preferably, the current head position is based on a position error signal (PES) and the head width is pre-stored data indicative of the physical or magnetic head width measured prior to disk drive operation.